1. Field of the Invention
The present invention relates generally to an antenna, and more particularly, to a small-size antenna that can be mounted in a portable communication terminal.
2. Description of the Related Art
With the advancement of recent semiconductor technologies and various communication technologies, small-size portable communication terminals have been developed. For example, devices having a wireless communication function include notebooks, Portable Multimedia Players (PMPs), cellular phones, navigation systems, etc.
Wireless communication services offered by the above-mentioned devices include broadcasting services (satellite and/or terrestrial Digital Multimedia Broadcasting (DMB)), communication services, Internet services, and the like. In particular, the broadcasting service, which can be used while a user moves, may be provided by a device having internal and external antennas.
The above-mentioned devices are portable and require antennas having a small size and a capability of high performance to utilize the various services described above. As a result, the devices have used internal antennas as a means for satisfying the size and design factors.
FIG. 1 is a diagram illustrating a conventional internal antenna. An internal antenna 100 includes a dielectric layer 110, and a radiant surface 130 formed on the dielectric layer 110.
The radiant surface 130 is excited by a power supply line provided in a horizontal direction of the dielectric layer 110. A coaxial cable (not shown) may be used as a connection cable. An internal conductor of the coaxial cable is electrically connected to the radiant surface 130.
The internal antenna 100 is applicable to portable communication terminals and therefore the dielectric layer 110 has a low dielectric constant due to size restrictions.
However, the dielectric layer 110 with the lower dielectric constant may induce varying radiant characteristics of an antenna, such as hand phantom or hand effect, in which a reception frequency band is shifted while a user's body contacts the terminal.
FIG. 2 illustrates an experimental result of a frequency band shift due to hand phantom of a conventional internal antenna. A dashed line illustrated in FIG. 2 denotes a graph showing a band of frequencies f1′ and f2′ that the internal antenna desires to receive. A solid line illustrated in FIG. 2 denotes a graph showing a band of frequencies f1 and f2 received by the internal antenna due to hand phantom or hand effect.
In order to minimize a variation in radiant characteristics of an internal antenna due to hand phantom, a part that frequently contacts a user may be separated as far as possible from a part that mounts the internal antenna, an external antenna may be used, and a wideband antenna may be used.
However, there are problems in applying these methods for suppressing hand phantom to portable communication terminals of a limited size.
Although the use of a dielectric layer having a high dielectric constant has been proposed, this also leads to problems such as an increase of loss, a decrease of a bandwidth, and creation of a parasitic parameter. Specifically, when a dielectric layer having a high dielectric constant considering a physical length of an antenna is used, a bandwidth of the antenna is decreased and a propagation loss of the antenna is increased.